Bipolar electrochemical flow battery systems are generally well known. See, for example, U.S. Ser. No. 189,363 entitled "Terminal Electrode", filed May 2, 1988, by J. Zagrodnik and G. Bowen (attorney docket 91872), the disclosure of which is hereby incorporated by reference.
A flow battery typically comprises a series of voltaic cells, a pump for pumping electrolyte through the cells, an electrolyte reservoir, a cooling element, and external load-attachment studs in electrical communication with terminal electrodes located at each end of the battery.
The cells are made up of a series of alternating electrodes and separators such that each cell comprises an electrode upon which the anodic reaction and the cathodic reaction takes place on opposite sides. An ion-permeable separator separates the anodic from the cathodic half-cell. Anolyte is pumped through each anodic half-cell and catholyte is pumped through each cathodic half-cell. There is no hydraulic communication between adjacent half-cells; an anode half-cell is disposed between each cathode half-cell and vice versa.
Maximizing power output, and hence minimizing parasytic power losses, from bipolar flow batteries is an important design objective. Power losses result when catholyte leaks into an anolyte half-cell or when anolyte leaks into a catholyte half-cell due to the reduction in electrochemical potential. Similarly, electrolyte leakage to the external surface of a battery results in power loss, in addition to the associated corrosion and handling problems. Thus, it is desirable to provide strong, leak-proof seals between separators and electrodes to properly contain electrolyte.
Shropshire et al., U.S. Pat. No. 4,164,068 (Aug. 14, 1979), discloses, at column 5, lines 24-62, bipolar carbon-plastic electrode structures and other cell elements stacked together to form an electrochemical cell-functional arrangement. Adjacent frames are arranged so that a projection or one element contacts the frame surface of the next element in the stack. After the elements are stacked, they are sealed to one another, for example, by blast welding or ultrasonic welding.
Other attempts have been made to seal battery components together through the use of bolts, adhesives, or solvents. However, adhesives have proven unsatisfactory because of their general incompatibility with polyolefins, a material often used in the construction of separator and electrode frames. Solvent welding reduces design flexibility and increases piece part production cost because both the electrode and separator frame are generally coated with solvent. The use of bolts is undesirable because electrolyte often leaks through the bolt holes and the electrode or separator frames.